The invention relates generally to antennas and, more particularly, to an antenna structure for positioning antennas to cover six sectors of a wireless communication cell.
A wireless communication network is generally divided into cells which are circular in shape and sized according to the range with which antennas located at a Base Station Transceiver System (BTS), centrally located within the cell, can transmit to and receive from mobile stations without interfering with signals transmitted in adjacent cells. Each mobile station operating within a cell requires a certain amount of bandwidth to operate and, because the total bandwidth of base antennas is limited, the number of mobile stations which can operate within a cell is limited.
To increase the number of mobile stations which can operate within a cell, cells are typically divided into three sectors, each of which sectors cover 120xc2x0 of the cell. Furthermore, to improve the reception of signals transmitted from mobile stations, two antennas are typically provided for each sector, such that each cell is provided with a total of six base antennas. Of the two antennas in each sector, one is a xe2x80x9cmainxe2x80x9d antenna and the other one is a xe2x80x9cdiversityxe2x80x9d antenna. The main antenna both transmits and receives signals to and from a mobile station in a respective sector, while the diversity antenna only receives signals from a mobile station. The diversity antenna is spaced apart from the main antenna to provide xe2x80x9cspace diversityxe2x80x9d so that if one of the two antennas is not able to receive a signal transmitted from a mobile station, which may result from an obstruction in the path of transmitted signal, then the other antenna may receive the signal. A structure for supporting the six antennas for each cell is typically configured as a triangular platform, each side of which supports two antennas for one of three sectors of a cell.
To further increase number of mobile stations which can operate within a cell, cells may be divided into six sectors. There are, however, a number of problems associated with dividing cells into six sectors. For example, a hexagon-shaped (i.e., six-sided) platform configured for supporting twelve antennas with two antennas on each side sufficiently spaced apart to provide diversity would be six times larger than a triangular platform which provides that same space diversity for three sectors. Such a larger platform would cost more to build and install, be more visibly conspicuous, be more susceptible to weather such as wind currents. A larger platform would also weigh more and may also require a stronger mast to support it. While a six-sector platform is being installed to replace a three-sector platform, downtime would also be incurred during which mobile stations in the cell would not be operable. Alternatively, if a smaller platform is used which compromises the space diversity, then signal quality is degraded.
Accordingly, a continuing search has been directed to the development of an antenna structure which would support a six sector cell with acceptable space diversity to maintain good signal quality, but which does not require that a new larger and more costly platform be installed, and possible a new mast also be installed, during which installation wireless communications in the cell would be interrupted.
The present invention, accordingly, provides an antenna structure which supports a six sector cell. The antenna structure of the present invention includes a platform defining at least six sectors having a vertex contained substantially within the platform. At least six dual polarized antennas are positioned on the platform for transmitting and receiving signals substantially in each of the at least six sectors, respectively.
In another aspect of the present invention, an antenna structure includes a platform defining an equal number of first sectors and second sectors, wherein each first sector is associated with one corresponding second sector to define a respective pair of sectors. Each respective pair of sectors includes a first main antenna and a first diversity antenna positioned in opposing first and second sectors of the respective pair of sectors, the first main antenna being configured for transmitting and receiving signals substantially only in the first sector, and the first diversity antenna being configured for receiving signals substantially only from the first sector. Each respective pair of sectors further includes a second main antenna and a second diversity antenna positioned in opposing first and second sectors of the respective pair of sectors, the second main antenna being configured for transmitting and receiving signals substantially only in the second sector, and the second diversity antenna being configured for receiving signals substantially only from the second sector.
By use of the present invention, capacity of a BTS may be increased by a factor of at least 1.7 without incurring high installation costs and interruption in service.